Method of manufacturing an electrode system

ABSTRACT

The invention relates to a method of manufacturing an electrode system having a monograin layer. On free grain surfaces of the monograin layer a first electrode layer is deposited. After a material-removing treatment, a deposition step is applied in which parts of enveloping layers of the grains and edges of cores of the grains adjoining pn-junctions are selectively covered with an insulating material and a second eletrode layer is deposited on parts of the cores of the grains not covered.

[56] References Cited United States Patent I [111 3,847,758 Te Velde[451 Nov. 12,1974

[ METHOD OF MANUFACTURING AN 3,040,416 6/1962 ELECTRODE SYSTEM 3.038.9526/1962 2,904,6l3 9/l959 [75] Inventor: Ties Siebolt Te Velde,Emmasingel,

Eindhoven, Netherlands Primary Examiner-John H. Mack [73] Asslgnee' gb gg Corporanon New Assistant ExaminerR. L. Andrews Attorney, Agent, orFirnz-Frank R. Trifari [22] Filed: Feb. 12, 1973 [2l] Appl. No.: 331,993

[57] ABSTRACT [30] Foreign Application Priority Data The inventionrelates to a method of manufacturing an Feb 19, Netherlands ele trodeystem having a monogram layer On free 7 grain surfaces of the monograinlayer a first electrode U-S. s R, layer is d posited a material removingtreat- 29/572 ment, a deposition step is applied in which parts of en-5/48, C23b 11/00, 301k 5/02 veloping layers of the grains and edges ofcores of the [58] Field of Search. 29/572; 204/181, 56 R,

204/15 with an insulating material and a second eletrode layer isdeposited on parts of the cores of the grains not covered. UNITED STATESPATENTS 3,575,823 4/1971 Gordon 204/15 8 Claims, 6 Drawing Figuresgrains adjoining pn-junctions are selectively covered PATENTEL nnv 1 2I974 SHEEI 10F 2 METHOD OF MANUFACTURING AN ELECTRODE SYSTEM Theinvention relates to a method of manufacturing an electrode systemhaving a monograin layer, in which grains of a semiconductor materialwith enveloping layers and cores of opposite conductivity types areembedded in a layer of binder in a substantially monograin layer over apart of the layer thickness, a first electrode layer for contacting theenveloping layers of the grains is deposited on one side of themonograin layer with free grain surfaces, a material-removing treatmentis used in which parts of the cores of the grains and parts of theenveloping layers of the grains are exposed, after which in a succeedingprocess step insulating material is provided on the exposed part and asecond electrode layer for contacting the cores of the grains isdeposited.

The invention furthermore relates to an electrode system manufactured bymeans of the method.

The said electrode systems may comprise monograin layers with grainsoperating as diodes, in which the first and the second electrode layerare deposited on oppositely located sides of the monograin layer.

One side of other electrode systems manufactured by means of theabove-mentioned method is often free from electrode layers to facilitatethe entrance and/or emanation of light. These electrode systems ar used,for example, in solar cells and in injection luminescent light sources.

In manufacturing the said electrode systems, the enveloping layers ofthe grains must be connected together and the cores of the grains mustbe connected together by electrode layers which may not contact eachother.

It is often difficult to fulfil this requirement since in thematerial-removing treatment both the cores of the grains and theenveloping layers of the grains are exposed; this holds good inparticular if one of the sides of the electrode system must be free fromcontact layers. For example, in a method of the type mentioned in thepreamble (see US. Pat. No. 3,040,416) an insulating layer is provided onthe first electrode layer and the material-removing treatment is appliedon the side of said layers and the material of the grains and thematerial of the first insulating layer must be matched to each other insuch manner and the material-removing treatment should be such that ofthe grains a part of the first electrode layer and a part of theenveloping layer of the grains is removed and between the grains thefirst insulating layer is removed over a greater part of the layerthickness without, however, entirely removing the first electrode layerfrom and between the grains.

After providing insulating material in the form of a second insulatinglayer on the exposed parts, a second material-removing treatment iscarried out in which the material of the grain and the material of thesecond insulating layer are to be removed to an equal extent so as to beable to deposit the second electrode layer which contacts the cores ofthe grains and is separated from the first electrode layer.

The materials of the two insulating layers and of the grains must beaccurately matched to each other and in addition very high requirementsare imposed upon the material-removing treatment so that theabovedescribed method is difficult and cumbersome and often does notproduce the desired result but results, for example, in shortcircuit.

One of the objects of the invention is to provide a novel method ofcontacting the cores of the grains and the enveloping layers of thegrainsin an insulated manner and furthermore to provide an improvementof the method described in the US. patent specification, as a result ofwhich the manufacture becomes easier and can be carried out in fewersteps. The invention is inter alia based on the recognition of the factthat the second material-removing treatment may be omitted when no moreinsulating material is used than is necessary for the insulation of thesecond electrode layer relative to the enveloping layers of grains.

Therefore, according to the invention, the method is characterized inthat in said process step the insulating material is selectivelyprovided on the exposed parts of the enveloping layers of the grains andon edges of the exposed parts of the cores of the grains adjoining thejunctions and parts of the cores of the grains not covered during theprovision of the insulating material are then contacted by depositingthe second electrode layer.

One of the advantages obtained is that a second material-removingtreatment may be omitted and it is achieved that the material-removingtreatment to be used can be particularly simple since no relief need beprovided in the monograin layer. Agrinding or polishing process ispreferably chosen as the materialremoving treatment.

By means of the method according to the invention, good results can beobtained in providing mutually insulated electrode'layers on the coresof the grains and on the enveloping layers of the grains, for example,in manufacturing the already stated electrode system the electrodelayers of which are deposited on either side of the monograin layer.

An insulating layer is preferably provided on the first electrode layerand the material-removing treatment is applied to both last-mentionedlayers, parts of the first electrode layer being exposed, saidlast-mentioned parts being covered during the selective provision of theinsulating material.

In a preferred embodiment of the method according to the invention, theinsulating material is provided by electrophoresis in that the exposedparts are contacted with a bath containing an insulating materialsuitable for electrophoretic coating and electrophoresis is carried outby giving the first electrode layer a voltage relative to the bath atwhich the junctions between the cores of the grains and the envelopinglayers of the grains are biased in the reverse direction.

In another preferred embodiment of the method according to the inventionthe insulating material is provided by electrochemical polymerization inthat the'exposed parts are contacted with a bath containing a materialwhich is converted into the insulating material byelectrochemicalpolymerization and polymerization is carried by givingthe first electrode layer a voltage relative to the bath at which thejunctions between the cores of the grains and the enveloping layers ofthe grains are biased in the reverse direction.

In the above preferred embodiments, the provision of the insulatingmaterial proceeds more slowly according as more material is provided andis finally discontinued automatically.

The insulating material is preferably provided on the monograin layerprior to the material-removing treatment and after the treatment theinsulating material is caused to swell so that the exposed parts of theenveloping layers of the grains and the edges of the exposed parts ofthe cores of the grains adjoining the junctions are covered.

Swelling may be carried out, for example, by a treatment with vapour ora solution with a swelling agent suitable for the insulating material.

The swelling agent may be removed, for example, by evaporation orextraction, in which insulating material remains in the place covereddue to the swelling.

When a grinding process is used as a materialremoving treatment, it isadvantageous when the grains project approximately equally far from thelayer of binder with their free grain surfaces. Therefore, the monograinlayer is preferably obtained prior to depositing the first electrodelayer in that the grains are provided as a substantially monograin layerin an adhesive layer on a substantially plane substrate and embedded inthe layer of binder, after which the monograin layer is separated fromthe substrate to obtain the side with the free grain surfaces.

Preferably the side with the free grain surfaces is then treated with aspecific solvent for the binder so as to enlarge the free grain surface.

It is achieved that the grains project approximately equally far fromthe layer of binder also in the case in which all the grains are notaccurately equally large.

The invention furthermore relates to an electrode system manufactured bymeans of the method according to the invention.

The invention will now be described in greater detail with reference toa drawing and a few examples.

In the drawing:

FIGS. 1 to 5 are diagrammatic sectional views of parts of an electrodesystem in successive stages of manufacture by means of preferredembodiments of the method according to the invention and FIG. 6 is adiagrammatic sectional view of a part of an electrode system in a stageof manufacture by means ofa variation of the method according to theinvention.

The manufacture will now be described of an electrode system having bothlayers on one side of the monograin layer, which systems are used insolar cells an injection luminescent light sources. An electrode system51 (see FIG. 5) with a monograin layer (11, 21) is manufactured, inwhich grains 11 having a size of approximately 50 um and consisting ofsemiconductor material, for example gallium phosphide, havingapproximately 5 pm thick enveloping layers 12 and cores 13 of oppositeconductivity types are embedded in a layer 21 of binder (see FIG. 3) ina substantially monograin layer over part of the layer thickness.

After implantation in the usual manner in the gallium phosphide grain ofions of an element which can cause the same conductivity type in thegallium phosphide as the enveloping layers of the grains have, a firstelectrode layer 41 (see FIG. 4) for contacting the enveloping layers of.the grains is deposited on one side 31 of the monograin layer (11, 21)with free grain surfaces, for example, by means of vapour deposition ofgold. An insulating layer 42, for example of polyurethane, is providedon the first electrode layer 41. By using a material-removing treatment,for which a grinding process is preferably chosen, parts 43 of the cores13 of the grains, cores 44 of the enveloping layers 12 of the grains andparts 45 of the first electrode layer 41 are exposed.

Insulating material 52 of materials to be described hereinafter isselectively provided in the form of a pattern of grains on the exposedparts 44 of the enveloping layers 12 of the grains, on the exposed parts45 of the first electrode layer 41 and on edges 54 of the exposed parts43 of the cores 13 of the grains adjoining the junctions 14.

Parts of the cores 13 of the grains not covered during the provision ofthe insulating material 52 are then contacted by depositing the secondelectrode layer 53. For that purpose, ions are implanted in a usualmanner in the gallium phosphide grains of an element which can cause thesame conductivity type in the gallium phosphide as the cores of thegrain have, and a second electrode layer 53 is deposited, for example,by vapourdepositing gold.

The first electrode layer 41 and the second electrode layer 53 can beprovided with current conductors in a usual manner.

When a grinding process is used as a materialremoving treatment, it isadvantageous when the grains project approximately equally far from thelayer of binder with the free grain surfaces.

Therefore, the monograin layer (11, 21) is obtained prior to depositingthe first electrode layer 41 by providing the grains 11 as a layer whichhas a thickness substantially of one grain in an adhesive layer 15 on asubstantially plane substrate 6 (see FIG. 1).

The adhesive layer 15 consists, for example, of a usual rubber glue andthe substrate 16 of glass. The grains 11 are embedded in the layer 21 ofbinder (see FIG. 2) which consists of an electrically insulatingmaterial, for example, polyurethane.

The monograin layer (11, 21) is then separated from the substrate 16 andthe side 31 with the free grain surfaces is obtained (see FIG. 3).

The free grain surface may still be enlarged by a treatment with aspecific solvent for a binder. in the case of polyurethane this can becarried out in a usual manner by a treatment with an alcoholic potassiumhydroxide solution.

EXAMPLE 1 In the first example the insulating material 52 is provided byelectrophoresis in that the exposed parts 43, 44, 45 are contacted witha bath containing an insulating material suitable for electrophoreticcoating.

Electrophoresis is carried out by giving the first electrode layer 41 avoltage relative to the bath at which the junctions 14 between the cores13 of the grains and the enveloping layers 12 of the grains are biasedin the reverse direction.

The grains consist, for example, of the semiconductor material galliumphosphide. By doping with zinc the cores 13 have been made p-typeconductive and by doping with sulfur the enveloping layers 12 have beenmade n-type conductive.

In a manner conventionally used in electrophoretic coating, a bath isused of a solution of a synthetic resin containing carboxyl groupsand/0r hydroxyl groups and of an organic amine or ammonia in water. Theweight concentration of solid of the solution is ID to l5 percent.Conventional materials such as epoxy-, acrylateor alkyl resins maybeused as a synthetic resin. A positive voltage of, for example,approximately +100 volt relative to the bath is given to the firstelectrode layer 41. During the passage of current through the bath, thecurrent rapidly decreases to a fraction, for example, 1 to percent ofthe original value, and the exposed parts 44, 45 and at most edges 54 ofthe exposed parts 43 of the cores 13 of the grains are covered. Theinsulating material reaches, for example, a layer thickness of 5 um. Theinsulating material is finally subjected to a baking treatment for 5 tominutes 120 to 180C. During providing the insulating material there mayalso be proceeded so that a certain current density is adjusted (in theorder of magnitude of 0.1 mA/cm and the process is discontinued when thevoltage has reached a certain high value.

EXAMPLE 2 The second example differs from the first example in that inthis case the insulating material 53 is provided by electrochemicalpolymerisation in that the exposed parts 43, 44, 45 are contacted with abath containing a material which is converted into the insulatingmaterial by electrochemical polymerisation. The polymerisation iscarried out by giving the first electrode layer 41 a voltage relative tothe bath at which the junctions 14 between the cores 13 of the grainsand the enveloping layers 12 of thegrains are biased in the reversedirection.

In a manner conventionally used in electrochemical polymerisation a bathis used having a mixture of orthoisopropylphenol and triethylamine in amolecular ratio of 10 1. At a positive voltage of +200 V of the firstelectrode layer 41 relative to the bath, insulating material 52 isprovided in a'thickness of 0.6 am. The current density decreases duringthe process from approximately 10' A/cm to approximately 10' A/cm":

EXAMPLE 3 The third example differs from the preceding examples in thatthe insulating material is provided on the monograin layer (11, 21)prior to the materialremoving treatment and the insulating materialafter the treatment is allowed to swell so that the exposed parts 45 ofthe first electrode layer 41, the exposed parts 44 of the envelopinglayers 12 of the grains and the edges 54 of the exposed parts 43 of thecores 13 of the grains adjoining the junctions 14 are covered (see FIG.6). Theinsulating material is provided, for example, as an insulatinglayer 42. As a material for the insulating layer 42 is used, forexample, polyurethane which swells by a treatment with vapour of ethylacetate.

After removing the ethyl acetate by evaporation at 80C,insulating-material52 remains in the places covered by the swelling.

The invention is not restricted to the examples described.

For example, instead of gallium phosphide another suitable semiconductormaterial, for example zinc selenide, mixed crystals of gallium arsenideand-gallium phosphide or mixedcrystalsof gallium arsenide and aluminiumarsenidemay be used. The cores of the grains may also show n-typeconductivity and the enveloping layers of the grains may show p-typeconductivity. -In the latter case, of course, the insulating materialused in the electrophoretic coating and the material used in theelectrochemical polymerisation must be adapted to the polarity of thefirst electrode layer varyingrelative to the bath. In the case ofelectrophoretic coating, for example, synthetic resins on the basis ofmelamine are to be considered. Upon providing insulating material bymeans of swelling it makes no difference whether the enveloping layersof the grains have p-type or ntype conductivity.

The method according to the invention may also be used in manufacturingelectrode systems in which the electrode layers are present onoppositely located sides of the monograin layer.

What is claimed is:

1. A method of manufacturing an electrode system having amonograinlayer, in which grains of a semiconductor material withenveloping layers and cores of opposite conductivity types are embeddedin a layer of binder in a substantially monograin layer over a part ofthe layer thickness, a first electrode layer for contacting theenveloping layers of the grains is deposited on one side of themonograin layer with free grain surfaces, a material-removing treatmentis used in which parts of the cores of the grains and parts of theenveloping layers of the grains are exposed, after which in a succeedingprocess step insulating material is provided on the exposed partsand asecond electrode layer for contacting the cores of the grains isdeposited, characterized in that in said process step the insulatingmaterial is selectively provided on the exposed parts of the envelopinglayers of the grains and on edges of the exposed parts of the cores ofthe grains adjoining the junctions and parts of thecores of the grainsnot covered during the provision of the insulating material are thencontacted by depositing the second electrode layer.

2. A method as claimed in claim 1, characterized in that an insulatinglayer is provided on the first electrode layer, the material-removingtreatment is applied to both last-mentioned layers, parts of the firstelectrode layer being exposed, said latter parts being covered duringthe selective provision of insulating material.

3. A method as claimed in claim 1, characterized in that the insulatingmaterial .is provided by electrophoresis in that the exposed parts arecontacted with a bath containing an insulating material suitable forelectrophoretic coating and electrophoresis is carried out by giving thefirst electrode layer a voltage relative to the bath at which thejunctions between the cores of the grains and the enveloping layers ofthe grains are biased in the reverse direction.

4. A method as claimed in claim 1, characterized in that the insulatingmaterial is provided by electrochemical polymerisation in that theexposed parts are contacted with a bath containing a material which isconverted into the insulating material by electrochemical polymerisationand polymerisation is carried out by giving the first electrode layeravoltage relative to the bath at which the junctions between the cores ofthe grains and the enveloping layers of the grains are biased in thereverse direction.

5. A method as claimed in claim 1, characterized in that the insulatingmaterial is provided on the monograin layer prior to thematerial-removing treatment and after the treatment the insulatingmaterial is caused to swell so that the exposed parts of the envelopinglaylayer on a substantially plane substrate and embedded in the layer ofbinder, after which the monograin layer is separated from the substrateto obtain the side with the free grain surfaces.

8. A method as claimed in claim 7, characterized in that the side withthe free grain surfaces is then treated with a specific solvent for thebinder so as to enlarge the free grain surface.

1. A METHOD OF MANUFACTURING AN ELECTRODE SYSTEM HAVING A MONOGRAINLAYER, IN WHICH GRAINS OF A SEMICONDUCTOR MATERIAL WITH ENVELOPINGLAYERS AND CORES OF OPPOSITE CONDUCTIVITY TYPES ARE EMBEDDED IN A LAYEROF BINDER IN A SUBSTANTIALLY MONOGRAIN LAYER OVER A PART OF THE LAYERTHICKNESS, A FIRST ELECTRODE LAYER FOR CONTACTING THE ENVELOPING LAYERSOF THE GRAINS IS DEPOSITED ON ONE SIDE OF THE MONOGRAIN LAYER WITH FREEGRAINS SURFACES, A MATERIAL-REMOVING TREATMENT IS USED IN WHICH PARTS OFTHE CORES OF THE GRAINS AND PARTS OF THE ENVELOPING LAYERS OF THE GRAINSARE EXPOSED AFTER WHICH IN A SUCCEEDING PROCESS STEP INSULATING MATERIALIS PROVIDED ON THE EXPOSED PARTS AND A SECOND ELECTRODE LAYER FORCONTACTING THE CORES OF THE GRAINS IS DEPOSITED CHARACTERIZED IN THAT INSAID PROCESS STEP THE INSULATING MATERIAL IS SELECTIVELY PROVIDED ON THEEXPOSED PARTS OF THE ENVELOPING LAYERS OF THE GRAINS AND ON EDGES OF THEEXPOSED PARTS OF THE CORES OF THE GRAINS ADJOINING THE JUNCTIONS ANDPARTS OF THE CORES OF THE GRAINS NOT COVERED DURING THE PROVISION OF THEINSULATING MATERIAL ARE THEN CONTACTED BY DEPOSITING THE SECONDELECTRODE LAYER.
 2. A method as claimed in claim 1, characterized inthat an insulating layer is provided on the first electrode layer, thematerial-removing treatment is applied to both last-mentioned layers,parts of the first electrode layer being exposed, said latter partsbeing covered during the selective provision of insulating material. 3.A method as claimed in claim 1, characterized in that the insulatIngmaterial is provided by electrophoresis in that the exposed parts arecontacted with a bath containing an insulating material suitable forelectrophoretic coating and electrophoresis is carried out by giving thefirst electrode layer a voltage relative to the bath at which thejunctions between the cores of the grains and the enveloping layers ofthe grains are biased in the reverse direction.
 4. A method as claimedin claim 1, characterized in that the insulating material is provided byelectrochemical polymerisation in that the exposed parts are contactedwith a bath containing a material which is converted into the insulatingmaterial by electrochemical polymerisation and polymerisation is carriedout by giving the first electrode layer a voltage relative to the bathat which the junctions between the cores of the grains and theenveloping layers of the grains are biased in the reverse direction. 5.A method as claimed in claim 1, characterized in that the insulatingmaterial is provided on the monograin layer prior to thematerial-removing treatment and after the treatment the insulatingmaterial is caused to swell so that the exposed parts of the envelopinglayers of the grains and the edges of the exposed parts of the cores ofthe grains adjoining the junctions are covered.
 6. A method as claimedin claim 1, characterized in that a grinding process or a polishingprocess is chosen as a material-removing treatment.
 7. A method asclaimed in claim 1, characterized in that prior to depositing the firstelectrode layer the monograin layer is obtained in that the grains areprovided as a substantially monograin layer in an adhesive layer on asubstantially plane substrate and embedded in the layer of binder, afterwhich the monograin layer is separated from the substrate to obtain theside with the free grain surfaces.
 8. A method as claimed in claim 7,characterized in that the side with the free grain surfaces is thentreated with a specific solvent for the binder so as to enlarge the freegrain surface.